Health Risk And Source Apportionment Of Heavy Metals In The Soil-rice System Of Jiulong River Basin

In the prevention and control of regional heavy metal pollution and the sustainable development of agricultural economy,it is important to systematically study the contents and distribution patterns of heavy metals in the agricultural soil-rice system,quantitatively analyze the source of heavy metals,and accurately and comprehensively assess the pollution levels and health risks of heavy metals.In this study,the pollution characteristics,sources apportionment and health risk assessment of heavy metals in the soil-rice system of the Jiulong River Basin were investigated by using various pollution evaluation methods,source analysis methods such as lead isotope and receptor models,heavy metal bioavailability and health risk evaluation models.The main results were as follows:(1)A variety of heavy metals had been enriched in agricultural soils of the Jiulong River Basin to different degrees,and the contents of Cd,Zn,Pb and Cu exceeded the soil pollution risk screening values in some areas.The spatial distribution of each heavy metal varies significantly.The speciation characteristics of each heavy metal varies greatly,among which Cd,Pb,Mn and Cu have higher bioavailability and higher potential biotoxicity.Combining various pollution evaluation methods,it was concluded that agricultural soils already had different degrees of heavy metals pollution.(2)There were individual exceedances of heavy metals in rice in the Jiulong River Basin.The distribution of each heavy metal in different tissues of rice plants varied significantly,and the migration of heavy metals was influenced by many factors.Linear and log-linear fitting were performed to establish a quantitative prediction model for heavy metals in the soil-rice system,which can better predict the level of heavy metals in soil-rice system.(3)The traditional multivariate statistical analysis method,receptor model and lead isotope tracing technique were combined to analyze the sources of heavy metals in agricultural soils and rice in the Jiulong River Basin.The result of PMF model showed that the average contributions of natural,agricultural,industrial and fossil fuel sources to heavy metals in agricultural soils in the Jiulong River basin were34.3%,22.2%,22.1% and 21.4%,respectively;while the average contributions to heavy metals in rice were 19.6%,30.0%,18.9% and 31.6%,respectively.The result of the lead isotope tracing technique showed that the average contributions of natural,agricultural,industrial and fossil fuel sources to lead in agricultural soils were 25.5%,35.3%,24.5% and 14.7%,respectively;while the average contributions to lead in rice were 4.8%,35.1%,6.0% and 54.1%,respectively.(4)Combining with the occurrence form and Pb isotopic composition of agricultural soils,the results showed that the residual fraction was more sensitive to the information of natural sources and the bioavailable fraction was more sensitive to the information of anthropogenic sources;The Pb from anthropogenic sources tends to exist in the soil in weakly acid-soluble state and reducible state;The Pb from different sources tends to exist in different forms,which can provide some information on the characteristics of Pb sources.(5)A health risk evaluation method based on PMF-SBET-HRA model was established.The results showed that the bioaccessibility of each heavy metal in rice was greater than that of the corresponding heavy metal in soil,which was more easily absorbed by human body,may have non-carcinogenic and carcinogenic risks;the non-carcinogenic risk was mainly contributed by As,while the carcinogenic risk was mainly contributed by Cd.The main sources of heavy metal health risks in the soil-rice system were agricultural and industrial sources,which generate health risks through the pathway of oral intake of food.(6)The transport characteristics of Pb in the "potential source-soil-rice" system were quantified by combining Pb isotope tracing technology and Iso Source software.The lead in agricultural soil-rice system was mainly from natural,agricultural,industrial and fossil fuel sources.After the anthropogenic lead was imported into agricultural soil,part of it migrated to the deep soil layer and existed in different forms.Partly of the Pb was enriched in the surface layer and may be absorbed by the rice roots.Most of the Pb which absorbed by the rice roots was accumulated in the roots and only a small part was transported to the stems.The anthropogenic lead may also be absorbed by the leaves of rice plants through the atmospheric pathway and partly transported to the stems and brown rice.